The present invention relates to an optical communication system for realizing a digital data bus for performing information communication between audio and video appliances.
FIG. 1 shows an example of a system construction of a digital data bus realized by electric communication using metallic wire as a transmission medium.
In FIG. 1, portions surrounded by broken lines designate terminal equipments which are connected to each other through metallic wire. In each terminal equipment, the reference numeral 3 designates a communication interface section for performing data communication according to a predetermined communication protocol. A driver circuit 1 and a receiver circuit 2 are connected to the communication interface section 3. The reference numerals 15 and 16 designate an input terminal and an output terminal respectively. The output terminal of each terminal equipment is connected to the input terminal of the succeeding terminal equipment through metallic wire successively to thereby constitute a bus-shaped transmission line. Because output signals from the respective terminal equipments can be simultaneously received by all of the terminal equipments through the bus-shaped transmission line, it is possible to perform channel access control based on surviving type CSMA/CD (Carrier Sense Multiple Access with Collision Detection). The reference numeral 17 designates terminal resistors which are provided on opposite ends of the bus for the purpose of impedance matching.
In the case of a digital data bus, wiring between terminal equipments becomes complex, because a data communication transmission medium must be newly provided in addition to a conventional medium for transmitting audio and video signals. Therefore, each terminal equipment may be constituted by a coupler for coupling a transmission signal with an up-load signal and a branch device for branching a reception signal from a down-load signal by use of optical fiber as a transmission medium to thereby facilitate multiple transmission of audio and video signals as well as digital data and conserving wiring between terminal equipments. However, a large insertion loss occurs in the branch device as well as in the coupler, so that the levels of signals between terminal equipments vary widely in the case of bus connection. Further, an increase in signal delay time is caused by an opto-electric converter section and an electro-optic converter section, so that there has been a limitation in transmission rate, in number of terminal equipments and in line length for realizing channel access control based on the surviving type CSMA/CD.